[Mesa-dev] [RFC] glsl: bump default glsl version to 130 if EXT_gpu_shader4 used

[Jason Ekstrand]

On Tue, May 15, 2018 at 1:38 PM, Marek Olšák <maraeo at gmail.com> wrote:

> On Tue, May 15, 2018 at 4:09 PM, Ilia Mirkin <imirkin at alum.mit.edu> wrote:
>
>> On Tue, May 15, 2018 at 3:54 PM, Marek Olšák <maraeo at gmail.com> wrote:
>> > On Tue, May 15, 2018 at 3:36 PM, Ilia Mirkin <imirkin at alum.mit.edu>
>> wrote:
>> >>
>> >> The extension is totally different... it adds things like "unsigned
>> >> int", and a ton of texture*/shadow* variants. If it helps this one
>> >> shader compile, that's a coincidence. IMO it's dangerous to start
>> >> throwing things like this in.
>> >
>> >
>> > That's why it prints a warning. The extension isn't exposed.
>>
>> It bumps the GLSL version to 1.30 though, which e.g. makes "in" and
>> "out" a keyword. And a bunch of other stuff like that. Just seems
>> dangerous.
>>
>
> It may seem dangerous, but not after you consider that it changes a
> compile failure into "some behavior" and a warning. That is pretty safe,
> because you'll either get a compile failure again, or you'll get correct
> behavior as if a subset of the extension was exposed. Either case is
> harmless.
>

This does seem really sketchy.  It's a spec violation because we are
required to fail the shader compile for unknown extensions.  And it's
letting a shader through even though we know it's likely to die in a fire
later on due to the fact that we only implement 30% of gpu_shader4.  On top
of that, the best justification we can come up with is a broken app that
assumes gpu_shader4 but doesn't actually use it.

Another option would be to allow drirc to force-enable GLSL extensions and
shader versions and use that to make the one app work.

--Jason
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